In the drilling and completion of oil wells, various types of fluids are used. The fluid of choice is a function of the subterrean formation, underground temperature, to what stage the drilling operation has proceeded, etc. Thus, an operator may use various drilling, workover, and completion fluids such as drilling muds, acidicing fluids, hydraulic fracturing fluids, and eventually cement prior to completing a hole. It is highly desirable that these fluids not intermix as one is replacing the other in the borehole and for this purpose spacer fluids are used. In formulating such spacer fluids for particular applications, the operator must prepare the fluids as so to be compatible with the two fluids being separated. Thus, density must be adjusted, cross-linking must be avoided, etc. Generally, such fluids comprise water, clay, and a polymer such as hydroxyethyl cellulose, polyacrylamides, guar gum derivatives, or xanthan gum.